It has long been known that physical activity has a great impact on our health. Now, new research comes to support that by saying that exercising between the ages of 12 and 35 cuts women’s risk of developing breast cancer.

Researchers at the Washington University School of Medicine in St. Louis and Harvard University in Boston evaluated questionnaires from 64,777 premenopausal women involved in the Nurses Health Study II. The women detailed their physical activity starting from the age 12 to the present.

The study found that the women whose activity equaled 13 walking hours a week or 3.25 running hours per week had a 23 percent lower risk of premenopausal breast cancer compared with the less active women. Within six years of enrolling, 550 women were diagnosed with breast cancer before menopause.

“We don't have a lot of prevention strategies for premenopausal breast cancer, but our findings clearly show that physical activity during adolescence and young adulthood can pay off in the long run by reducing a woman's risk of early breast cancer,” said lead researcher Graham Colditz, professor and associate director of prevention and control at the Alvin J. Siteman Cancer Center at Washington University School of Medicine and Barnes-Jewish Hospital.

Colditz further added that the findings should be “one more reason to encourage young girls and women to exercise regularly.”

Women’s risks to develop breast cancer often include factors that are unchangeable such as how early they start menstruating, how late menopause hits, family history of the disease. But physical activity and body weight are two factors that women can control, this way protecting themselves against breast cancer.

“I'd say you and your daughter are getting off the couch. Women who engage in physical activity not only during adolescence but during adulthood lower their risk,” Dr. Alpa Patel, a cancer prevention specialist at the American Cancer Society, who praised the new research, said as quoted by the Associated Press.

Although death rates from breast cancer have been declining, possibly due to earlier detection and diagnosis, on a national level, breast cancer still represents the second leading cause of cancer death for women. The first cause is lung cancer. According to the American Cancer Society, more than 180,000 American women are diagnosed with breast cancer every year, and almost 41,000 will die because of it.

The results of the study, funded by grants from the National Cancer Institute and the American Cancer Society, were published in the May 13 issue of the Journal of the National Cancer Institute.